With rapid development of industrial technologies around the world, problems of energy shortage and environmental pollution are increasingly serious, and the hybrid power technology is regarded as one of the effective solutions for solving the problems of energy shortage and environmental pollution. A wheeled crane mostly travels in urban areas or among cities, but due to influence of road environment, frequent starting, acceleration, braking and climbing occur in the travelling process. In addition, the crane is heavy, and has a higher speed relative to other engineering machinery vehicles, so use of the traditional mechanical friction braking manner will cause waste of a large amount of kinetic energy. In the current automobile industry, mostly used is the oil-electric hybrid power technology, which is generally applied to limousines and buses but is not applicable to such super-tonnage engineering vehicle as the wheeled crane due to cost and driving force problems. In consideration that many hydraulic systems have the same characteristics as electric systems in some aspects, oil-hydraulic hybrid power becomes another choice for super-tonnage load-carrying vehicles. The wheeled crane has certain advantages in the aspect of oil-hydraulic hybrid power due to its own hydraulic system, so the oil-hydraulic hybrid power application for vehicle travelling can be accomplished by only slight system modification, and furthermore, the hydraulic system also can be applied to hoisting power for an upper structure.
However, during the research of applying oil-hydraulic hybrid power to the wheeled crane, it is found that the hydraulic system often has a large operating torque and its performance is not easy to control. When the hydraulic system is applied to a multi-gear vehicle, it is very likely to cause large influence on the vehicle if output control of the braking force and the driving force is unreasonable, and particularly when the difference of gear speed ratios is large, the difference of required torques is large too. Therefore, the demand-control concept of the torque of the hybrid power system is proposed, which is desired to be helpful in some extent in improving the travelling stability of the wheeled crane added with the parallel-type oil-hydraulic hybrid power system. Currently, domestic research on oil-hydraulic hybrid power is not deep enough, and particularly oil-hydraulic hybrid power has not been applied to such an engineering machinery product as the wheeled crane. Some mentioned control methods and steps are mostly applications of oil-electric hybrid power or applications of oil-hydraulic hybrid power to other engineering machinery vehicles.
The torque control method in the prior art is summarized as follows:
A throttle pedal signal and a current vehicle speed signal are obtained through collection by a sensor, then the obtained throttle signal and vehicle speed signal are calculated and through calculation, a target driving torque of the vehicle is determined, and finally respective output torques of an engine and a motor are determined according to a certain algorithm. Such a control method ignores the influence of gears, without considering the problem that different gears generate power impact on a vehicle, and such a problem is particularly obvious for a hybrid power system with a front engine, which will reduce the service life of the hybrid power system and cause certain influence on driving comfort of a driver at the same time and driving safety is also affected.
In the prior control method steps, since hybrid power control is not actually made to such a vehicle as the wheeled crane, some characteristics of the crane itself are not considered, for example, the crane has large inertia, relatively high speed and many gears, and in the prior method, the problems of power impact generated in processes of energy storage and release and driving comfort of the driver are not considered.
First, the crane has many forward gears and generally employs a multi-gear box, and correspondingly speed ratios of a gearbox are greatly different between a high gear and a low gear. For a hybrid power system with a front engine, the same torque provided by a secondary element will be increased by several or a dozen of times after being transferred to a transmission shaft, thus will generate a bigger power impact; Second, in the prior method steps, it is also not considered that at the moment of energy release completion, the problem of instantaneous driving force reduction due to sudden disappearance of the driving torque provided by the secondary element will cause power impact, which not only does not conform to the operation habit of the driver but also influences the driving comfort of the driver, and seriously, it will even influence judgment of the driver and affect safety;
Third, in the prior art method, the influence of the rotating speed on a recovery process is not considered. In the energy recovery process, the rotating speed of the secondary element is gradually reduced along with gradual energy recovery, when the rotating speed is reduced to the minimum effective rotating speed, a control program will turn off the secondary element to enable the displacement of the secondary element to return to zero, and if sudden turning off results in sudden reduction of an actual vehicle braking torque, the driver will feel vehicle jitter obviously, and even the driving safety will be influenced.